I. Field of the Invention
This invention relates generally to trailer jacks used to support the tongue of a trailer when the trailer is not coupled to a towing vehicle, and more particularly to a trailer jack allowing for rapid deployment.
II. Description of the Prior Art
A typical trailer jack is used to support the tongue weight of a trailer when the trailer hitch is not fastened to a towing vehicle and generally comprises an upper, outer tube adapted to be coupled to the trailer tongue and a lower inner tube coupled in telescoping relation to the upper outer tube and incorporating a lead screw member that is journaled for rotation in the upper, outer tube about a longitudinal axis thereof. The lead screw is threaded into a traveling nut that is welded to the inner wall of the lower, inner tube so that when the lead screw is rotated by a crank, the lower inner tube can be made to project further from or retract back into the lumen on the upper outer tube, depending on the direction of rotation of the crank. A disadvantage of this type of jack is that it takes many rotations of the crank to move the lower tube between a retracted disposition needed to provide ground clearance when the trailer is being towed and an extended disposition needed to elevate the trailer tongue when decoupling the trailer tongue receiver from the ball hitch of the towing vehicle.
The Ryan U.S. Pat. No. 2,939,679 addresses this problem by providing a tension spring that is operatively coupled between the upper and lower tubes, allowing a user to step down on a footplate affixed to a bottom end of the lower tube to rapidly move the footplate against the ground and lock the lower tube in its extended position. At this point, only a few turns of the crank are needed to raise the trailer tongue sufficiently to uncouple the trailer from the towing vehicle. When it is desired to retract the lower tube into the upper one, when the lock is released, the tension spring works against gravity to lift the foot sufficiently to provide the needed ground clearance. Because the jack of the '679 patent comprises only two telescoping tubes, it is unduly long and cumbersome.
The McMahan U.S. Pat. No. 8,091,922 teaches another way of obtaining a fast initial adjustment of the jack, followed by a final adjustment using a lead screw where the final adjustment makes it only necessary to make a few turns of the screw to achieve a desired elevation. The jack is comprised of an inner tubular member nested within an outer tubular member, a collar, a housing and a pin. The inner member is threadedly connected to the outer member with a bolt having a crank attached at one end. The bolt enables incremental adjustments in the trailer height by extension and refraction of the inner member with respect to the outer member. The connected outer and inner members are secured to the trailer with a pin inserted through the housing, a hole in the collar and one of a plurality of longitudinal holes in the outer member. To create rapid gross adjustment in the trailer height, the pin is retracted, a different hole in the outer member is registered with the hole in the collar and the pin is then reinserted. Having a plurality of longitudinally spaced holes in the outer member necessarily weakens the structural integrity of the jack.
The Wilson U.S. Pat. No. 4,769,864 describes a trailer jack having a tubular outer housing adapted to be attached to a trailer vehicle with second and third tubular members slidably disposed therein. A locking mechanism is provided adjacent an aperture in a wall of the second tubular member for positioning a pin in selectively alignable apertures in a wall of the third tubular member, thereby preventing relative movement between the second and third tubular members. A tension spring engages both the second and third tubular members, the spring being located within the third tubular member. It functions to bias the third tubular member toward a retracted position with respect to the second tubular member. A crank is provided for rotating a threaded screw member for moving the second tubular member with respect to the tubular outer housing.
The present invention is deemed to be an advancement over the prior art in affording an improved releasable locking arrangement that affords greater selectivity over the initial positioning of the lower tubular member with respect to the intermediate member.